Radio apparatus, and method and program for controlling spatial path

ABSTRACT

A PDMA terminal ( 1000 ) establishes communication by forming a plurality of spatial paths to another single radio apparatus. A plurality of antennas constituting an array antenna are divided into a plurality of subarrays corresponding to the plurality of spatial paths respectively. An adaptive array processing unit (USP) can perform an adaptive array processing for each of the plurality of subarrays. A memory (MMU) stores in advance information on the number of antennas associated with the number of spatial paths that can be formed by the array antenna. A control unit (CNP) controls a processing to transmit possible multiplicity information to another radio apparatus at a prescribed timing.

This application is a continuation application of U.S. patentapplication Ser. No. 13/786,888, filed on Mar. 6, 2013, which is acontinuation of U.S. patent application Ser. No.13/098,878, filed on May2, 2011, which is a divisional of U.S. patent application Ser. No.12/463,657, filed on May 11, 2009, which is a divisional of U.S. patentapplication Ser. No. 10/508,655, filed on Sep. 22, 2004, which is a U.S.National Phase under 35 U.S.C. §371 of International Application No.PCT/JP2003/002883, filed on Mar. 11, 2003, which is based upon andclaims priority based on 35 USC 119 from prior Japanese PatentApplication No. 2002-081375, filed on Mar. 22, 2002; the entire contentsof which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a radio apparatus, and a method and aprogram for controlling a spatial path, and more particularly to a radioapparatus capable of establishing multiplex communication between oneradio terminal and a radio base station via a plurality of paths formedby space division, as well as to a method and a program for controllinga spatial path.

BACKGROUND ART

Recently, as a communication scheme for a rapidly developing mobilecommunication system, for example, PHS (Personal Handy phone System), aTDMA scheme in which 1 frame (5 ms) consisting of respective 4 slots (1slot: 625 μs) for transmission and reception is regarded as a base unithas been adopted. Such a communication scheme for PHS is standardized asthe “second generation cordless communication system,” for example.

A signal of 1 frame is divided into 8 slots, that is, first 4 slotsserve for reception, while following 4 slots serve for transmission, forexample.

Each slot consists of 120 symbols. For example, in a signal of 1 frame,assuming that one reception slot and one transmission slot form onepair, three pairs of slots are allocated as traffic channels for threeusers, and remaining one pair of slots is allocated as a controlchannel, respectively.

In the PHS system, in a control procedure for establishingsynchronization, a link channel is initially established by the controlchannel, followed by a processing for measuring an interference wave (anundesired wave: U wave). In addition, after a processing for settingcommunication condition by the allocated channel, speech communicationis started. Such a procedure is disclosed in detail in Personal HandyPhone System RCR Standard RCR STD-28 (published by Association of RadioIndustries and Businesses), which is a standard of PHS.

FIG. 19 shows a flow in such a communication sequence in PHS. In thefollowing, brief description thereof will be provided with reference toFIG. 19.

First, a C channel (control channel: CCH) is used to transmit a linkchannel establishment request signal (LCH establishment request signal)from a PHS terminal to a base station. A PHS base station detects anempty channel (empty traffic channel: empty T channel) (carriersensing), and uses the C channel to transmit a link channel allocationsignal (LCH allocation signal) designating an empty T channel to the PHSterminal.

In the PHS terminal, whether or not an interference wave signal having apower larger than a prescribed level is received is measured in thedesignated T channel (U wave measurement) based on link channelinformation received from the PHS base station. When the interferencewave signal with a power larger than a prescribed level is not detected,that is, when other PHS base station does not use the designated Tchannel, the PHS terminal uses the designated T channel to transmit asynchronous burst signal to the base station. Meanwhile, the basestation sends back a synchronous burst signal to the terminal.Synchronization is thus established.

On the other hand, when an interference wave signal having a powerlarger than a prescribed level is detected in the designated T channel,that is, when the T channel is being used by other PHS base station, thePHS terminal repeats the control procedure from the link channelestablishment request signal.

In this manner, in the PHS system, a traffic channel between a terminaland a base station is connected, using a channel where the interferencewave is weak and excellent communication performance is attained.

In the PHS, a PDMA (Path Division Multiple Access) scheme has beenimplemented, in which, in order to enhance an efficiency in utilizing afrequency of a radio wave, mobile radio terminal units (terminals) of aplurality of users establish spatial multiple connection to a radio basestation (base station) through a plurality of paths formed by spatiallydividing an identical time slot of an identical frequency.

The PDMA scheme adopts an adaptive array technique, for example. In anadaptive array processing, based on a reception signal from a terminal,a weight vector consisting of reception coefficients (weights) forrespective antennas in the base station is calculated for adaptivecontrol, and a signal from a desired terminal is accurately extracted.

With such an adaptive array processing, an uplink signal from theantenna of each user terminal is received by the array antenna of thebase station, and then separated and extracted with receptiondirectivity. A downlink signal from the base station to the terminal istransmitted from the array antenna with transmission directivity to theantenna of the terminal.

Such an adaptive array processing is a well-known technique, anddescribed in detail, for example, in Nobuyoshi Kikuma, “Adaptive SignalProcessing by Array Antenna”, Kagaku Gijutsu Shuppan, pp. 35-49,“Chapter 3: MMSE Adaptive Array” published on Nov. 25, 1998. Therefore,description of its operation principle will not be provided.

FIG. 20A is a conceptual view schematically illustrating an example inwhich one terminal 2 with a single antenna is connected to a PDMA basestation 1 via one of a plurality of paths formed by space division in amobile communication system (PHS) adopting the PDMA scheme.

More specifically, PDMA base station 1 receives an uplink signal fromone antenna 2a of terminal 2 with an array antenna 1a, and the signal isseparated and extracted with reception directivity through theabove-described adaptive array processing. On the other hand, arrayantenna 1a of PDMA base station 1 transmits a downlink signal withtransmission directivity to one antenna 2a of terminal 2. Terminal 2receives the downlink signal with its antenna 2a without adaptive arrayprocessing.

FIG. 20B is a timing chart schematically showing a manner of channelallocation in this example. In the example of FIG. 20B, users 1 to 4establish time-division multiplexed to respective time slots obtained bydivision in a direction of time axis at an identical frequency. Here,one user is allocated to each slot via one path in a spatial direction.

Identification of a desired signal out of signals received in the PDMAscheme is performed in the following manner. A radio wave signaltransmitted/received between a terminal such as a mobile phone and abase station is transmitted in what is called a frame configurationincluding a plurality of frames. For example, each frame includes atotal of 8 slots, that is, 4 slots for uplink communication and 4 slotsfor downlink communication. Broadly speaking, the slot signal isconstituted of a preamble consisting of a signal sequence already knownto a reception side, and data (such as voice) consisting of a signalsequence unknown to the reception side.

The signal sequence in the preamble includes a signal train (referencesignal: unique word signal, for example) of information for discerningwhether or not a sender is a desired party for the reception side toestablish communication. For example, an adaptive array radio basestation performs weight vector control (determines weight coefficient)so as to extract a signal that seems to include a signal sequencecorresponding to a desired party, based on comparison of the receivedsignal sequence with the unique word signal taken out from a memory.

In addition, each frame is assumed to have a configuration in which aunique word signal (reference signal) section described above isincluded and cyclic redundancy check (CRC) is enabled.

In contrast, an MIMO (Multi Input Multi Output) scheme has beenproposed, in which multiplex communication is established between oneterminal having a plurality of antennas and a PDMA base station via aplurality of spatial paths of an identical frequency and an identicaltime slot.

Communication technologies for such MEMO scheme are described in detail,for example, in Nishimura et al., “SDMA Downlink Beamforming for a MIMOChannel,” Technical Report of MICE, A-P2001-116, RCS2001-155, pp. 23-30,October 2001, and in Tomisato et al., “Radio Signal Processing forMobile MIMO Signal Transmission,” Technical Report of IEICE, A-P2001-97,RCS2001-136, pp. 43-48, October 2001.

FIG. 21 is a conceptual view schematically illustrating an example inwhich one terminal PS1 with two antennas establishes spatial multipleconnection to a PDMA base station CS1 via a plurality of paths (e.g. twopaths) PTH1, PTH2 formed by space division in the mobile communicationsystem (PHS) adapted to such MIMO scheme.

More specifically, PDMA base station CS1 receives uplink signals fromrespective two antennas 12a, 12b of terminal CS1 with an array antenna11a, and the signals are separated and extracted with receptiondirectivity through the above-described adaptive array processing.

On the other hand, array antenna 11a of PDMA base station CS1 transmitsdownlink signals with transmission directivity to respective twoantennas 12a, 12b of terminal PS1. Terminal PS1 receives correspondingdownlink signals with its respective antennas without adaptive arrayprocessing.

FIG. 22 is a timing chart schematically showing a manner of channelallocation in this example. In the example of FIG. 22, users 1 to 4 aretime-division multiplexed to respective time slots divided in adirection of time axis at an identical frequency. An identical user isallocated in a manner of multiple connection to each slot via two pathsin a spatial direction.

For example, noting a first time slot in FIG. 22, user 1 is allocated toall channels via two spatial paths. Then, a signal of user 1 is dividedand transmitted between the terminal and the base station via two pathsin the identical slot, and the divided signals are reconfigured on thereception side. Two-paths-for-one-user scheme as shown in FIG. 22 candouble a communication speed, as compared with one-path-for-one-userscheme in FIG. 20B.

Here, some of the plurality of spatial paths in the identical slot inthe PDMA scheme may be used to establish communication inmultiple-paths-for-one-user scheme as shown in FIG. 21. Concurrently,remaining paths may be used to establish communication inone-path-for-one-user scheme as shown in FIGS. 20A and 20B.

A specific method of transmission/reception of a signal in the MIMOscheme as shown in FIG. 21 is disclosed in detail in Japanese PatentLaying-Open No. 11-32030, for example.

In the MIMO scheme as shown in FIG. 21, the terminal side preparesantennas in the number corresponding to the number of paths to be set,so as to establish communication.

If a failure occurs on a propagation path, however, there is no degreeof freedom in that path allowing for avoiding such a failure.Eventually, disconnection of the path has been likely.

In this manner, though improvement in the communication speed can beexpected with the conventional MIMO scheme in an environment where acondition for communication is excellent, it is difficult in some casesto achieve a stable communication speed.

Accordingly, an object of the present invention is to provide a radioapparatus capable of adaptive modification in connection of a pluralityof paths between a terminal and a base station in accordance with acommunication condition in a mobile communication system wherecommunication is established with a multiple-paths-for-one-user schemesuch as the MIMO scheme, as well as a method and a program forcontrolling a spatial path.

DISCLOSURE OF THE INVENTION

According to one aspect of the present invention, a radio apparatus canestablish communication by forming a plurality of spatial paths toanother single radio apparatus. The radio apparatus includes a pluralityof antennas constituting an array antenna, and the plurality of antennasare divided into a plurality of subarrays corresponding to the pluralityof spatial paths respectively. The radio apparatus further includesadaptive array means capable of adaptive array processing for each ofthe plurality of subarrays; storage means for storing in advanceinformation on possible multiplicity associated with a number of spatialpaths that can be formed by the array antenna; and control means forcontrolling a processing to transmit the information on possiblemultiplicity to another radio apparatus at a prescribed timing.

Preferably, the information on possible multiplicity is information on atotal number of the plurality of antennas.

Preferably, the radio apparatus further includes monitor means fordetecting a communication status for each of the plurality of antennas.The information on possible multiplicity is information associated witha maximum number of spatial paths that can be used for multiplexcommunication, determined based on a detection result by the monitormeans.

Preferably, the monitor means detects a number of antennas that canattain normal reception, and the information on possible multiplicity isinformation on a maximum number of antennas that can attain normalreception.

Preferably, a signal transmitted/received by the radio apparatus isdivided into a plurality of frames. The monitor means detects an errorrate for each frame in each spatial path. The information on possiblemultiplicity is information on a number of spatial paths that can beused for multiplex communication.

Preferably, the monitor means detects an amount of interference betweenthe spatial paths, and the information on possible multiplicity isinformation on a number of spatial paths that can be used for multiplexcommunication.

Preferably, the adaptive array processing means can change a combinationof the antennas allocated to each subarray to perform the adaptive arrayprocessing. The control means divides the plurality of antennas into aset or sets in a number corresponding to a number of paths, inaccordance with the number of paths notified from another radioapparatus, to implement the set or sets of the antennas as eachsubarray.

Preferably, the adaptive array processing means can change a combinationof the antennas allocated to each subarray to perform the adaptive arrayprocessing. The control means allocates one antenna out of the pluralityof antennas to respective subarray or subarrays in a numbercorresponding to the number of paths notified from another radioapparatus, and subsequently allocates remaining antennas out of theplurality of antennas to each of the subarrays in a prescribed order.

Preferably, the control means preferentially allocates the antennashaving an identical plane of polarization to an identical subarray.

Preferably, the radio apparatus further includes means for detecting areception level for each antenna. The control means preferentiallyallocates the antennas having planes of polarization different from eachother to an identical subarray.

Preferably, the adaptive array processing means can change a combinationof the antennas allocated to each subarray to perform the adaptive arrayprocessing. The radio apparatus further includes monitor means formonitoring communication quality for each spatial path duringcommunication. The control means changes the number of the antennasallocated to each subarray in accordance with a detection result of themonitor means.

According to another aspect of the present invention, a method ofcontrolling a spatial path in a radio apparatus capable of communicationby forming a plurality of spatial paths to another single radioapparatus is provided. The radio apparatus includes an array antennaconstituted of a plurality of antennas that can be divided into aplurality of subarrays corresponding to the plurality of spatial pathsrespectively, and adaptive array means capable of adaptive arrayprocessing for each of the plurality of subarrays. The method includesthe steps of storing in advance information on possible multiplicityassociated with a number of spatial paths that can be formed by thearray antenna; transmitting the information on possible multiplicity toanother radio apparatus from the radio apparatus at a prescribed timing;and determining the antenna to be allocated to the subarray based oninformation specifying the number of the spatial paths provided fromanother radio apparatus.

Preferably, the method of controlling a spatial path further includesthe step of detecting a number of antennas capable of normal receptionin the radio apparatus. The information on possible multiplicity isinformation on a maximum number of antennas that can attain normalreception.

Preferably, a signal transmitted/received by the radio apparatus isdivided into a plurality of frames. The method further includes the stepof detecting an error rate for each frame for each of the spatial pathsin the radio apparatus. The information on possible multiplicity isinformation on a number of spatial paths that can be used for multiplexcommunication.

Preferably, the method of controlling a spatial path further includesthe step of detecting an amount of interference between the spatialpaths in the radio apparatus. The information on possible multiplicityis information on a number of spatial paths that can be used formultiplex communication.

Preferably, the step of determining the antenna includes the step ofdividing the plurality of antennas into a set or sets in the numbercorresponding to a number of paths, in accordance with the number ofpaths notified from another radio apparatus, to allocate the set or setsof the antennas to each subarray.

Preferably, the step of determining the antenna includes the step ofallocating one antenna out of the plurality of antennas to respectivesubarray or subarrays in a number corresponding to the number of pathsnotified from another radio apparatus, followed by allocating remainingantennas out of the plurality of antennas to each subarray in aprescribed order.

Preferably, in the step of allocating antennas to the subarray, theantennas having an identical plane of polarization are preferentiallyallocated to an identical subarray.

Preferably, in the step of allocating antennas to the subarray, theantennas having planes of polarization different from each other arepreferentially allocated to an identical subarray.

According to yet another aspect of the present invention, a program forcontrolling a spatial path in a radio apparatus capable of communicationby forming a plurality of spatial paths to another single radioapparatus is provided. The radio apparatus includes an array antennaconstituted of a plurality of antennas that can be divided into aplurality of subarrays corresponding to the plurality of spatial pathsrespectively, and adaptive array means capable of adaptive arrayprocessing for each of the plurality of subarrays. The program causes acomputer to execute the steps of: storing in advance information onpossible multiplicity associated with a number of spatial paths that canbe formed by the array antenna; transmitting the information on possiblemultiplicity to another radio apparatus from the radio apparatus at aprescribed timing; and determining the antenna to be allocated to thesubarray based on information specifying the number of the spatial pathsprovided from another radio apparatus.

Preferably, the method of controlling a spatial path further includesthe step of detecting a number of antennas capable of normal receptionin the radio apparatus. The information on possible multiplicity isinformation on a maximum number of antennas that can attain normalreception.

Preferably, a signal transmitted/received by the radio apparatus isdivided into a plurality of frames. The method further includes the stepof detecting an error rate for each frame for each of the spatial pathsin the radio apparatus. The information on possible multiplicity isinformation on a number of spatial paths that can be used for multiplexcommunication.

Preferably, the method of controlling a spatial path further includesthe step of detecting an amount of interference between the spatialpaths in the radio apparatus. The information on possible multiplicityis information on a number of spatial paths that can be used formultiplex communication.

Preferably, the step of determining the antenna includes the step ofdividing the plurality of antennas into a set or sets in a numbercorresponding to a number of paths, in accordance with the number ofpaths notified from another radio apparatus, to allocate the set or setsof the antennas to each subarray.

Preferably, the step of determining the antenna includes the step ofallocating one antenna out of the plurality of antennas to respectivesubarray or subarrays in a number corresponding to the number of pathsnotified from another radio apparatus, followed by allocating remainingantennas out of the plurality of antennas to each subarray in aprescribed order.

Preferably, in the step of allocating antennas to the subarray, theantennas having an identical plane of polarization are preferentiallyallocated to an identical subarray.

Preferably, in the step of allocating antennas to the subarray, theantennas having planes of polarization different from each other arepreferentially allocated to an identical subarray.

Therefore, according to the present invention, in a terminal or a basestation in the mobile communication system adapted to the MIMO scheme,communication in each spatial path is established by antennas dividedinto subarrays. As the antennas adapted to each path or the number ofpaths are adaptively controlled in accordance with a communicationstatus, stable communication in the MIMO scheme can be achieved.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram showing a configuration of a PDMAterminal 1000 adapted to an MIMO scheme in a first embodiment of thepresent invention.

FIG. 2 is a conceptual view illustrating a state in which PDMA terminal1000 according to the present invention and a PDMA base station CS1 arecommunicating with each other.

FIG. 3 is a flowchart illustrating an operation for notifying basestation CS1 of information on the number of antennas from terminal 1000.

FIG. 4 is a schematic block diagram illustrating a configuration of aPDMA terminal 1200 in a variation of the first embodiment of the presentinvention.

FIG. 5 is a schematic block diagram illustrating a configuration of aPDMA terminal 2000 in a second embodiment of the present invention.

FIG. 6 is a schematic block diagram illustrating a configuration of aPDMA terminal 2200 in a first variation of the second embodiment of thepresent invention.

FIG. 7 is a flowchart showing a flow in adaptive control of the numberof paths to be set in PDMA terminal 2000 or PDMA terminal 2200.

FIG. 8 is a flowchart showing a method of adaptive control of the numberof paths to be set with regard to terminal 2000 in a second variation ofthe second embodiment.

FIG. 9 shows a configuration in which four antennas #1 to #4 arearranged in a notebook personal computer 3000.

FIG. 10 is a conceptual view illustrating an arrangement of fourantennas attached to a mobile phone terminal 4000.

FIG. 11 is a flowchart illustrating an operation when antennas having anidentical plane of polarization are selected for a subarray.

FIG. 12 is a flowchart illustrating another method of allocating aplurality of antennas of a terminal to each path.

FIG. 13 is a schematic block diagram illustrating a configuration of aPDMA terminal 5000.

FIG. 14 is a flowchart illustrating an operation of a control circuitCNP and a subarray selector 32.

FIG. 15 is a flowchart illustrating a processing for allocating antennasin terminal 5000 to respective paths based on a reception level.

FIG. 16 is a flowchart illustrating another method of allocating eachantenna to each path based on the reception level.

FIG. 17 is a conceptual view illustrating a configuration before andafter a combination of antennas constituting a path is changed.

FIG. 18 is a conceptual view illustrating a state after a combination ina subarray is changed as a result of detection of deterioration incommunication quality as shown in FIG. 17.

FIG. 19 shows a flow of a communication sequence in PHS.

FIGS. 20A and 20B are conceptual views illustrating an example in whichone terminal 2 with a single antenna is connected to a PDMA base station1 via one of a plurality of paths formed by space division.

FIG. 21 is a conceptual view illustrating an example in which oneterminal PS1 with two antennas establishes spatial multiple access toPDMA base station CS1 via paths PTH1, PTH2 formed by space division.

FIG. 22 is a timing chart schematically showing a manner of channelallocation.

BEST MODES FOR CARRYING OUT THE INVENTION

In the following, embodiments of the present invention will be describedin detail with reference to the figures. It is noted that the samereference characters refer to the same or corresponding components inthe figures.

(First Embodiment)

FIG. 1 is a functional block diagram showing a configuration of a PDMAterminal 1000 adapted to the MIMO scheme in a first embodiment of thepresent invention.

Referring to FIG. 1, PDMA terminal 1000 includes: transmission/receptionunits TRP1 to TRP4 providing transmission signals to an array antennaconstituted of a plurality of antennas #1 to #4 or receiving receptionsignals; a signal processing unit USP subjecting signals fromtransmission/reception units TRP1 to TRP4 to adaptive array processingfor separating and extracting a signal from a base station duringcommunication, and adjusting an amplitude and a phase of thetransmission signal so as to form transmission directivity to the basestation during communication; a modulation unit MDU for modulating asignal provided to signal processing unit USP; a demodulation unit DMUfor demodulating a signal from signal processing unit USP; a controlunit CNP controlling a baseband signal provided to modulation unit MDUand a baseband signal provided from demodulation unit DMU, andcontrolling an operation of PDMA terminal 1000; and a memory MMU forholding information of the number of antennas for PDMA terminal 1000(hereinafter, referred to as “antenna number information”).

Here, a processing such as an adaptive array processing, a modulationprocessing, a demodulation processing, or a control processing performedby PDMA terminal 1000 can be performed, individually or as an integratedprocessing, with software by means of a digital signal processor.

Transmission/reception unit TRP1 includes a transmission unit TP1 forprocessing a high-frequency signal in transmission, a reception unit RP1for processing a high-frequency signal in reception, and a switch unitSW1 for switching connection between antenna #1 and transmission unitTP1 or reception unit RP1 in accordance with a transmission mode or areception mode. Other transmission/reception units TRP2 to TRP4 areconfigured in a similar manner.

When terminal 1000 is a PC card mounted to a personal computer, a signalfrom control circuit CNP may be output to the personal computer mountedwith terminal 1000 via a not-shown interface. Alternatively, whenterminal 1000 is an independent communication terminal, for example, amobile phone, the signal from control circuit CNP may be provided to aprocessor for voice signal processing or the like within terminal 1000.

In the description above, though the number of antennas has been set to4, more generally, it may be set to N (N: natural number). As describedbelow, though the number of spatial paths for communication with thebase station (hereinafter, simply referred to as “path”) with respect tothe number of antennas is set to 2, communication can be establishedwith the possible number of paths in accordance with the number ofantennas.

For example, it is assumed that the number of antennas is set to 4, andthe number of paths is set to 2. Then, two series of adaptive arrayprocessing units corresponding to the two paths respectively should onlybe provided in advance in signal processing unit USP. When there arelarger number of antennas or paths, similarly, adaptive array processingunits in the number corresponding to respective paths should only beprovided. In addition, if a combination of the antennas processed byeach series should be changed, each series of adaptive array processingunits and the antennas connected thereto should only be switched undercontrol of control unit CNP.

FIG. 2 is a conceptual view illustrating a state in which PDMA terminal1000 according to the present invention and PDMA base station CS1 arecommunicating with each other.

As shown in FIG. 2, PDMA terminal 1000 has four antennas #1 to #4. PDMAterminal 1000 forms one path to base station CS1 with directivity bymeans of antennas #1 and #3, and forms another path to base station CS1with transmission/reception directivity by means of antennas #2 and #4.For example, though not limited to such an example, a plurality ofspatial paths for communication can be formed by formingtransmission/reception directivity described above by utilizing the factthat an identical signal reaches PDMA terminal 1000 via differentpropagation paths due to an influence of buildings in a communicationpath.

For example, in terminal 1000 having four antennas, two subarraysserving as two-element adaptive array respectively are implemented insetting two paths with the array antenna. Here, two-element adaptivearray reception and transmission is performed in one subarray.

As described above, memory MMU within terminal 1000 stores the “antennanumber information”. Therefore, terminal 1000 transmits the antennanumber information to base station CS1 at a prescribed timing. Basestation CS1 issues an instruction for the number of paths to be set tobase station 1000 based on the antenna number information from terminal1000. Terminal 1000 sets the number of paths to be formed in accordancewith the instruction from base station CS1.

FIG. 3 shows a flow illustrating an operation for notifying base stationCS1 of the antenna number information from terminal 1000 in such amanner.

In FIG. 3, solely a portion required for transmitting/receivinginformation between terminal 1000 and base station CS1 in a controlprocedure for establishing synchronization in a common PHS systemdescribed in connection with FIG. 19 is extracted for representation.

First, the antenna number information is transmitted to the base stationfrom terminal 1000 as control information in requesting establishment ofa link channel (LCH allocation request).

Base station CS1 gives an instruction for the number of paths statingthat the number of paths to be set should be equal to or smaller thanthe number of antennas, as the control information for link channelallocation instruction, for example, based on the antenna numberinformation from the terminal.

In succession, terminal 1000 transmits a synchronous burst signal tobase station CS1 using a designated traffic channel (T channel), and thebase station also sends back a synchronous burst signal to the terminal.Synchronization is thus established. Thereafter, the traffic channel (Tchannel) is activated based on the established synchronization, andcommunication is started.

Here, the base station adaptively modifies the number of paths set byterminal 1000 in accordance with the status during communication, andterminal 1000 is notified of a resultant value as the controlinformation during communication.

Though the timing of notification of the antenna number information fromterminal 1000 to base station CS1 has been set at the time of request ofestablishing the link channel in the description above, it may be at acontrol information stage during establishing the traffic channel (TCH),or alternatively, the antenna number information may be notified fromterminal 1000 to base station CS1 as the control information after thetraffic channel is established.

With the above-described configuration, in terminal 1000, a plurality ofsubarrays formed by dividing a plurality of antennas constituting anarray antenna can control communication in one path establishingcommunication with base station CS1. Accordingly, the path can be formedin a flexible manner in accordance with a change in communication statusbetween base station CS1 and terminal 1000. Therefore, even if thecommunication status is varied, stable multiplex communication can beachieved via a plurality of spatial paths of an identical frequency andan identical time slot.

(Variation of First Embodiment)

FIG. 4 is a schematic block diagram illustrating a configuration of aPDMA terminal 1200 in a variation of the first embodiment of the presentinvention.

PDMA terminal 1200 in a second embodiment is different from PDMAterminal 1000 in the first embodiment shown in FIG. 1 in that terminal1200 includes an antenna abnormal state detector ADP capable ofdetecting abnormality in a communication status for each antenna uponreceiving communication information from each antenna #1 to #4.

As PDMA terminal 1200 is otherwise configured in a manner similar toPDMA terminal 1000, the same reference characters are given to the sameor corresponding components and description thereof will not berepeated.

In terminal 1200, memory MMU stores not only the antenna numberinformation, but also information on an antenna in an abnormal state(the number of antennas in an abnormal state and an abnormal antennaidentifier) from antenna abnormal state detector ADP. Based on suchinformation, terminal 1200 transmits the information on the number ofantennas capable of normal transmission/reception to the base station ata prescribed timing similar to that in the first embodiment.

Base station CS1 determines the number of paths to be set based on theantenna number information from terminal 1200 indicating the maximumnumber of antennas capable of normal transmission/reception, andnotifies terminal 1200 of the number of paths at a timing similar tothat in the first embodiment.

With the above-described configuration, a plurality of spatial paths canbe established without using antennas incapable of normaltransmission/reception due to a status of hardware, communicationstatus, or the like among the plurality of antennas, and stablemulti-input multi-output multiplex communication can be achieved.

(Second Embodiment)

FIG. 5 is a schematic block diagram illustrating a configuration of aPDMA terminal 2000 in a second embodiment of the present invention.

PDMA terminal 2000 is different from PDMA terminal 1000 shown in thefirst embodiment in that a signal from demodulation unit DWU is providedto an FER counter 22 detecting a frame error rate.

FER counter 22 counts the number of errors in a signal frame for eachpath. A resultant frame error rate (FER), which is an error rate perframe, is stored in memory MMU as one of elements in communicationquality information for evaluating communication quality.

The demodulated signal of which errors are counted in FER counter 22 isprovided to control unit CNP, which communicates with memory MMU, refersto the communication quality information of the downlink signal such asan FER held in memory MMU, and performs control of an uplink spatialpath with a method of controlling a spatial path according to thepresent invention described later.

Here, a processing such as an adaptive array processing, a modulationprocessing, a demodulation processing, or a control processing,performed by PDMA terminal 2000 can be performed, individually or as anintegrated processing, with software by means of a digital signalprocessor.

Terminal 2000 notifies base station CS1 of quality information for eachspatial path acquired in a manner described above and held in MMU, orinformation on the antenna currently allocated to each path at aprescribed timing similar to that in the first embodiment.

Though the information held in memory MMU has been assumed as theantenna number information or FER data in the description above, not thenumber of antennas themselves but the FER data and the maximum number ofpaths P_MAX that can be formed in terminal 2000 determined from the FERdata described above may be stored in MMU, for example.

(First Variation of Second Embodiment)

FIG. 6 is a schematic block diagram illustrating a configuration of aPDMA terminal 2200 in a first variation of the second embodiment of thepresent invention.

PDMA terminal 2200 is different from PDMA terminal 2000 in the secondembodiment shown in FIG. 5 in that an interference measurement device 24for measuring an amount of interference from another path with respectto a signal input to demodulation unit DMU is provided instead of FERcounter 22, and memory MMU stores the information on communicationquality in a path based on the amount of interference and information onantenna allocation, that is, how antennas are currently allocated toeach path.

In this manner, based on the information on communication quality in thepath and the information on antenna allocation stored in memory MMU,terminal 2200 notifies base station CS1 of the number of paths availablefor communication at a prescribed timing similar to that in the firstembodiment.

Interference measurement device 24 measures an interference componentcontained in a complex reception signal input to the demodulationcircuit.

In a method of measurement, an error component e(t) between a complexreception signal y(t) and a reference signal d(t) stored in memory MMUis calculated, and a power of that error signal component is regarded asa power of the interference signal.

Here, e(t) and the interference power are expressed in the followingequations:e(t)=y(t)−d(t)(interference power)=Σ|e(t)|/Twhere T represents an observation time (or reference signal length).

With the above-described configuration as well, the communicationquality for each path can be ascertained in terms of an amount ofinterference, and an effect as in the second embodiment can be obtained.

(Operation in Second Embodiment or First Variation of Second Embodiment)

FIG. 7 is a flowchart showing a flow in adaptive control of the numberof paths set in PDMA terminal 2000 in the second embodiment described inconnection with FIG. 5 or PDMA terminal 2200 in the first variation ofthe second embodiment described in connection with FIG. 6.

In the following, an operation of PDMA terminal 2000 in the secondembodiment will basically be described, and subsequently, differencefrom the operation of PDMA terminal 2000 will be described with respectto an operation of PDMA terminal 2200 in the first variation of thesecond embodiment.

Referring to FIG. 7, first, terminal 2000 notifies base station CS1 ofthe number of antenna elements N in the terminal or the maximum numberof paths P_MAX (step S100).

In terminal 2000, the total N antennas are used to form one subarray,and one path is set for communication (step S102).

In succession, in terminal 2000, communication quality is evaluated bythe FER for each path. It is determined whether FERs of all paths areequal to or smaller than a prescribed threshold value, whether thenumber of paths that can be set has not yet been attained, and whetheror not the communication speed is insufficient (step S104).

Here, the expression that “communication speed is insufficient” meansthat, when an amount of data to be transferred is compared with thecurrent communication speed, transfer is not completed in a sufficientlyshort period of time in terminal 2000 with respect to a processing of anapplication during execution, for example.

When it is determined in step S104 that, with regard to thecommunication quality for each path and the number of paths that can beset, the number of paths can further be increased and the communicationspeed is insufficient, notification that an increase in the number ofpaths P by 1 is desired is transmitted from terminal 2000 to basestation CS1 (step 106).

Then, when terminal 2000 receives permission for setting from basestation CS1 (step S108), terminal 2000 increases the number of paths tobe set by 1. In response, terminal 2000 selects P (P=P+1) subarrays forcommunication (step S110), and the processing returns to step S104

On the other hand, when it is determined in step S104 that thecommunication status is poor or the communication speed is sufficient,or when permission for setting from the base station is not received instep S108, communication is performed with the current number of pathsfor a prescribed time period (step S112), and the processing returns tostep S104.

With the above-described processing, while the number of paths to be setfor multi-input multi-output communication is adaptively modified,communication between base station CS1 and terminal 2000 can beestablished. While maintaining excellent communication quality andexcellent communication speed, communication in the MIMO scheme can beattained.

It is to be noted in FIG. 7 that the number of antennas is in principledivisible by the number of paths designated by the base station.

In other words, the number of antennas in the antenna set (subarray)transmitting/receiving an identical signal to be set is obtained bydividing the total number of antennas by the number of paths to be set.

For example, when a terminal has a total of 4 antennas and two paths areset, two pairs (subarrays) each formed with two antennas are prepared.

Then, each subarray performs transmission/reception in each path.

In an operation of terminal 2200 in the first variation of the secondembodiment, in step S104, the communication quality of the path isevaluated not based on the FER value for each path but based on theamount of interference for each path.

(Second Variation of Second Embodiment)

In a second variation of the second embodiment described below, unlikeFIG. 7, a method of adaptive control of the number of paths to be set,which is applicable even when the number of paths designated by the basestation cannot divide the number of antennas, will be described.

Such an operation can also be processed in terminal 2000 and terminal2200.

FIG. 8 is a flowchart showing a method of adaptive control of the numberof paths to be set with regard to terminal 2000 in the second variationof the second embodiment.

Referring to FIG. 7, terminal 2000 notifies base station CS1 of thenumber of antenna elements N in the terminal. Alternatively, the maximumnumber of paths P_MAX may be notified (step S200).

In terminal 2000, one antenna is used to set one path (the number ofpaths P is set to 1) for communication (step S202).

In succession, in terminal 2000, it is determined whether FERs of allpaths on terminal side are equal to or smaller than a prescribedthreshold value, that is, the communication status is determined to beso excellent as to allow increase in the number of paths, whether thecurrent number of paths has not yet reached the number of paths that canbe set, whether or not the communication speed is insufficient, andwhether or not an antenna element which is not yet allocated to the pathis present (step S204).

When the conditions in step S204 are satisfied, notification thatincrease in the number of paths P by 1 is desired is transmitted fromterminal 2000 to base station CS1 (step S206).

When terminal 2000 receives permission for setting from base station CS1(step S208), terminal 2000 increases the number of paths to be set by 1(P←P+1), and P antennas are selected to start communication (step S210),and the processing returns to step S204.

When the conditions in step S204 are not satisfied, or when permissionfor setting from base station CS1 is not received in step S208, whetheror not an antenna which is not set for a path is present is determined(step S212). When an antenna which has not been set is remaining, oneantenna element is further allocated to a path which is determined tohave attained a quality lower than a prescribed level, so as to form asubarray (step S214).

In succession, communication is performed with the current number ofpaths P for a prescribed time period (step S216), and the processingreturns to step S204.

On the other hand, when there is no remaining antenna which has not beenset for a path in step S212, the processing moves to step S216.

In other words, in the second variation of the second embodiment, thenumber of antennas for each subarray is determined in the followingmanner. One antenna is first allocated to each set path. Then, amongremaining antennas, an additional antenna is sequentially allocated toeach path in accordance with the path identifier or the antennaidentifier while determining necessity for the increase in the number ofantennas. For example, when all subarrays are provided with two antennaseach, remaining antennas are again allocated. With such a process, eachsubarray performs transmission/reception in each path.

With above-described allocation of antennas to each path, the optimalnumber of antennas can be arranged for each path even when the number ofantennas is not necessarily divisible by the number of paths whichperform transmission/reception between base station CS1 and terminal2000. Communication in the MIMO scheme is thus enabled.

In an operation of terminal 2200 in the first variation of the secondembodiment, in step S104, the communication quality of the path isevaluated not based on the FER value for each path but based on theamount of interference for each path.

(Third Embodiment)

In the first and second embodiments, an arrangement of antennas used inthe MIMO scheme has not been limited in particular.

In a third embodiment, a configuration in which further improvement inthe communication quality is attained by employing a specificarrangement of a plurality of antennas will be described.

FIG. 9 shows a configuration in which four antennas #1 to #4 arearranged for a notebook personal computer 3000.

Antennas #1 and #3 are arranged on opposing ends of a display 3010 ofnotebook personal computer 3000, and antennas #2 and #4 are arranged onopposing ends of a keyboard. Here, in such a spatial arrangement of theantennas, antennas #1 and #3 operate as antennas in an identical planeof polarization (vertical polarization), while antennas #2 and #4operate as antennas in an identical plane of polarization (horizontalpolarization).

FIG. 10 is a conceptual view illustrating an arrangement of fourantennas attached to a mobile phone terminal 4000.

When a plurality of types of antenna elements are incorporated in mobilephone terminal 4000, as shown in FIG. 10, antennas #1 and #3 arearranged longitudinally and in parallel on opposing ends of a display4010 so as to have an identical plane of polarization (verticalpolarization), while antennas #2 and #4 are arranged so as to have anidentical plane of polarization (horizontal polarization) with display4010 and operation buttons 4020 interposed.

Though not specifically limited, antennas #1 and #3 arrangedlongitudinally may be whip antennas, while antennas #2 and #4 may beinverted-F shaped antennas.

In addition, antennas of the same type such as a chip antenna or a patchantenna may be arranged so as to form a set with respect to theidentical plane of polarization.

In the above-described configuration, selection of antennas for forminga subarray may be made such that antennas with the identical plane ofpolarization form an identical subarray. Here, when a set of antennasconstituting a subarray is selected in the second embodiment or thefirst variation of the second embodiment, or when a subarray is formedby sequentially allocating remaining antennas as described in the secondvariation of the second embodiment, antennas with the identical plane ofpolarization are allocated to an identical subarray.

By constituting one subarray with antennas having the identical plane ofpolarization in such a manner, the following effect can be obtained.

Under a condition of normal radio wave propagation, a path of anincoming radio wave tends to be spatially different if the plane ofpolarization is different. On the other hand, in order to obtain arraygain with an adaptive array, sufficient array gain cannot be obtained ifthere is a great level difference between reception signals.

Therefore, in selecting a subarray when two subarrays are both availablefor communication, antennas which have the identical plane ofpolarization, that is, antennas which are expected to have approximatelythe same reception levels are selected, whereby sufficient array gaincan be obtained.

In other words, constituting a subarray with antennas with the identicalplane of polarization is particularly effective in an example in whichvariation in the reception levels of four antennas is observed due todifferent planes of polarization, though the reception levels thereofare all higher than the minimum reception level.

FIG. 11 is a flowchart illustrating an operation when antennas having anidentical plane of polarization are selected for a subarray.

Referring to FIG. 11, terminal 3000 (or terminal 4000) notifies basestation CS1 of the number of antenna elements N (step S300).

In succession, the number of paths M set by base station CS1 is sentback, which is received by mobile terminal 3000 (or terminal 4000) (stepS302).

In mobile terminal 3000 (or terminal 4000), the number of antennas N isdivided by the number of paths M, and the resultant value n is set asthe number of antenna elements in a subarray. Here, antennas having theidentical plane of polarization are selected as antenna elementsconstituting an identical subarray (step S504).

If the number of antennas with the identical plane of polarization isnot an integer multiple of the number of antennas n in a subarray,remaining antennas may be allocated to other subarrays.

Then, a channel adapted to the multi-input multi-output scheme (MIMOchannel) is set for each subarray between mobile terminal 3000 (orterminal 4000) and base station CS1 for communication (step S306).

With the above-described allocation process of the antennas,communication is achieved by a subarray constituted of a set of antennasimplemented by preferentially selecting antennas with the identicalplane of polarization for each spatial path.

FIG. 12 is a flowchart illustrating another method of allocating aplurality of antennas in a terminal to each path.

Referring to FIG. 12, first, terminal 3000 (or terminal 4000) notifiesbase station CS1 of the number of antenna elements N (step S400).

In succession, the number of paths M set by the base station is sentback, which is received by mobile terminal 3000 (or terminal 4000) (stepS402). Mobile terminal 3000 (or terminal 4000) includes an antenna grouphaving x types (x≥M) of planes of polarization. Here, M antennas areselected and allocated to subarrays respectively such that correspondingplanes of polarization are not overlapped with one another (step S404).

In succession, a value of a variable na is set to 1 (step S406). Inaddition, whether an unallocated antenna is present or not isdetermined. When an unallocated antenna is present (step S408), theunallocated antenna is allocated to a subarray having na antennas. Here,the unallocated antenna is allocated such that the plane of polarizationthereof is identical to that of the antenna already contained in thesubarray (step S410).

Next, it is determined whether there is no longer an antenna that can beallocated on the basis of the identical plane of polarization. If anantenna to be allocated on that basis is still present (step S412), thevalue of variable na is incremented by 1 (step S414), and the processingreturns to step S408.

On the other hand, when there is no antenna that can be allocated on thebasis of the identical plane of polarization (step S412), an unallocatedantenna is allocated to a subarray having na antennas (step S416). Then,the value of variable na is incremented by 1 (step S414), and theprocessing returns to step S408.

When there is no longer an unallocated antenna in step S408, an MIMOchannel is set for each subarray for communication (step S420).

With the above-described allocation process of the antennas as well,communication is achieved by a subarray constituted of a set of antennasimplemented by preferentially selecting antennas with the identicalplane of polarization for each spatial path.

(Fourth Embodiment)

The third embodiment has described an example in which antennas havingthe identical plane of polarization constitute a subarray.

Depending on a communication status, however, enhancedtransmission/reception performance can be obtained when the subarray isconstituted of antennas having different planes of polarization.

Such an example will be described in the following.

In the third embodiment, in selecting antennas for forming a subarray,for example, a set of antennas can be selected so that antennas havingreception levels or antenna gains proximate to one another are locatedin an identical subarray. Alternatively, the reception level is measuredfor each antenna in advance and antennas are ranked in terms of thereception level. The antennas can be allocated to a subarray so thatantennas in a high rank in terms of the reception level are not unevenlydistributed in a specific subarray.

Here, when a set of antennas constituting a subarray is selected in thesecond embodiment or the first variation of the second embodiment, orwhen a subarray is formed by sequentially allocating remaining antennasas described in the second variation of the second embodiment, antennashaving reception levels or antenna gains proximate to one another areallocated to an identical subarray.

Under a condition of normal radio wave propagation, a path of anincoming radio wave will spatially be different if the plane ofpolarization is different. Accordingly, if something crosses thepropagation path of the radio wave between the terminal and the basestation, a phenomenon called “shadowing” in which reception power in acommunication path abruptly falls may occur, when the communication pathis formed solely by antennas with the identical plane of polarization.

If shadowing occurs, in some cases, the reception power in the path mayabruptly fall as low as a level at which communication is difficult. Insuch a case, communication in that path may be disconnected. Therefore,in a communication environment in which shadowing often takes place, itis desirable to locate antennas with different planes of polarization inthe identical subarray. With such a configuration of a subarray, even ifthe reception level of an antenna with a specific plane of polarizationfalls to a level disabling communication, an antenna with a differentplane of polarization can maintain a level allowing reception.Accordingly, communication in all communication paths can be maintained.

As such, in control unit CNP, it is possible to selectively employ amethod of constituting a subarray as described in the third embodimentand a method of constituting a subarray described below, in accordancewith a degree of stability in path multiplicity and by comparing acurrent communication status and an allocation state of antennas to asubarray.

FIG. 13 is a schematic block diagram illustrating a configuration of aPDMA terminal 5000 capable of selecting antennas constituting a subarraybased on information on the reception level or the plane of polarizationas described above.

PDMA terminal 5000 is different from PDMA terminal 1000 in the firstembodiment shown in FIG. 1 in that a reception level measurement device30 capable of measuring a reception level for each antenna with respectto reception signals from respective antennas #1 to #4 is provided, ameasurement result of the reception level measurement device is providedto control unit CNP, and control unit CNP causes memory MMU to storeinformation on the reception level.

In addition, memory MMU stores not only the measurement result of thereception level, but also information on the plane of polarization ofthe antenna and information on occurrence of communication disruptionseemingly caused by shadowing. In response, a subarray selector 32notifies control circuit CNP of a set of antennas to be selected as asubarray, from the information on the plane of polarization of theantenna, the information on shadowing or the like stored in the memory.

In other words, reception level measurement device 30 measures thereception level for each antenna. Control circuit CNP measures receptionlevel data for each antenna for a prescribed period of time, andmeasures “shadowing information” such as duration or frequency of a casein which reception is disabled for each antenna. Such results are storedin memory MMU. Subarray selector 32 selects a pair (or a set) ofantennas to be selected as a subarray, from the shadowing informationand the information on the plane of polarization in each antenna inmemory MMU.

FIG. 14 is a flowchart illustrating an operation of control circuit CNPand subarray selector 32 among the operations described above.

First, control circuit CNP measures the reception level for each antennain reception level measurement device 30, and measures duration orfrequency of a case in which reception is disabled (shadowinginformation) for each antenna. Such results are stored in memory MMU(step S500).

Then, control unit CNP determines whether or not shadowing exceeds aprescribed reference (step S502).

Here, though not limited in particular, “a prescribed reference” refersto a determination reference such as whether or not shadowing lasting atleast for a prescribed duration (0.5 second) occurs with a frequencymore than a prescribed level (two times/60 seconds), for example.

When it is determined that shadowing exceeds the prescribed reference instep S302, subarray selector 32 selects antennas with different planesof polarization as an identical subarray (step S504).

On the other hand, when it is determined that shadowing does not exceedthe prescribed reference in step S502, subarray selector 32 selectsantennas with an identical plane of polarization as an identicalsubarray (step S506). Selection of a subarray in this case may followthe procedure described with reference to FIG. 11 or 12.

FIG. 15 is a flowchart illustrating a processing for allocating antennasin terminal 5000 to each path based on a reception level, when antennashaving different planes of planarization are selected as an identicalsubarray in step S504 shown in FIG. 14.

First, terminal 5000 notifies base station CS1 of the number of antennaelements N (step S600).

In succession, terminal 5000 is notified of the number of paths M to beset from base station CS1 (step S602).

Terminal 5000 includes an antenna group having x types (x≥M) of planesof polarization. Terminal 5000 ranks the antennas in accordance withreception sensitivity (levels of signals from a base station to beconnected). Then, antennas are allocated to each subarray so thatantennas in a high rank in terms of the reception sensitivity are notunevenly distributed in a specific subarray, that is, an average of thereception levels is proximate to each other in each subarray, forexample (step S604).

An MIMO channel is set for each subarray constituted in theabove-described manner for communication (step S606).

With the method described above, stable communication adapted to theMIMO scheme can be achieved even in the communication environment whereshadowing frequently takes place.

Here, antennas having the reception level or the reception sensitivityproximate to each other may preferentially be allocated to an identicalsubarray in step S604 so that the reception level or the receptionsensitivity of antennas are balanced in forming a spatial path.

(Fifth Embodiment)

The third and fourth embodiments have described the arrangement of theantennas in a terminal and how antennas are allocated to each subarrayin accordance with the communication status in initiating communicationin the MIMO scheme.

Meanwhile, even after communication in the MIMO scheme is once started,it is also possible to control communication in the MIMO schemeadaptively in accordance with the communication status, by changingantennas allocated to a subarray in accordance with a change in thecommunication status in each spatial path.

Here, the communication status in each spatial path may refer to the FERfor each spatial path described with reference to FIG. 5, or an amountof interference for each spatial path described in connection with FIG.6, or alternatively, change with time in the reception level for eachantenna described with reference to FIG. 13.

FIG. 16 is a flowchart illustrating another method of allocating eachantenna to each path based on the reception level.

For example, when it is determined based on FER or the interferencevalue that the communication quality in a path PA has deterioratedduring communication (step S700), quality in a path other than path PAis checked, and whether or not the number of antenna elements in asubarray corresponding to that other path can be reduced is determined(step S702).

When a path capable of maintaining quality even if the number of antennaelements is reduced is present (step S704), one antenna in a subarraycorresponding to the path capable of maintaining quality even if thenumber of antenna elements is reduced is selected.

A selection reference here is chosen from a plurality of referencesbelow by setting priority among them in advance. Alternatively, one ofthe plurality of references below may be chosen as a reference.

(1) An antenna having a plane of polarization identical to that of anantenna already contained in the target subarray is selected.

(2) An antenna having a reception level proximate to that of an antennaalready contained in the target subarray is selected.

(3) An antenna having reception sensitivity proximate to that of anantenna already contained in the target subarray is selected.

(4) An antenna is selected randomly or in the order of antennaidentifier.

An antenna selected in such a manner is incorporated in the subarraycorresponding to the path in which quality has deteriorated (step S706).

Alternatively, when there is no path for which the number of antennascan be reduced in step S704, the processing in step S706 is notperformed but communication is maintained in current state.

FIG. 17 is a conceptual view illustrating a configuration before andafter a combination of antennas forming a path is changed in theabove-described manner.

Before changing the combination, antennas #1 and #3 form one path, whileantennas #2 and #4 form one path. Here, antennas #1 and #3 may have anidentical plane of polarization, while antennas #2 and #4 may have anidentical plane of polarization. Alternatively, a configuration in whicha set of antennas #1 and #3 and a set of antennas #2 and #4 formsubarrays respectively may minimize a difference in the reception levelsbetween the two sets.

Here, it is assumed that deterioration in the communication quality inpath PA formed by antennas #2 and #3 has been determined.

FIG. 18 is a conceptual view illustrating a state after a combination ina subarray is changed as a result of detection of deterioration incommunication quality as shown in FIG. 17.

As shown in FIG. 18, for example, antenna #3 is incorporated in a pathPB, antennas #2, #3 and #4 form one path, and antenna #1 alone performstransmission/reception in path PA.

In this manner, even if the communication quality is deteriorated, thenumber of antennas constituting the sub array is changed so as tomaintain desired communication quality, thereby enablingtransmission/reception in the MIMO scheme.

Here, a processing such as an adaptive array processing, a modulationprocessing, a demodulation processing, or a control processing performedby any PDMA terminal described above can be performed, individually oras an integrated processing, with software by means of a digital signalprocessor.

As described above, according to the present invention, in a terminal ora base station in a mobile communication system adapted to the MIMOscheme, communication in each spatial path is established by antennasdivided into subarrays. As the antennas corresponding to each path orthe number of paths are adaptively controlled in accordance with acommunication status, stable communication in the MIMO scheme can beachieved.

Industrial Applicability

The present invention is useful in a mobile communication system adaptedto the MIMO scheme, because stable communication can be achieved byadaptively controlling the antennas corresponding to each path or thenumber of paths in accordance with a communication status, in a terminalor a base station in a mobile communication system adapted to the MIMOscheme.

The invention claimed is:
 1. A radio apparatus for communication byforming a plurality of spatial signals to another radio apparatus,comprising: a plurality of transmission units connectable to a pluralityof antennas; at least a signal processing unit capable of processingspatial signals to be transmitted through the plurality of transmissionunits and the plurality of antennas; storage means for storing inadvance information on the number of spacial signals that can beprocessed by the signal processing unit, wherein the number of availablespacial signals is smaller than or equal to the total number of theplurality of antennas; control means for controlling a process oftransmitting the information on the number of spatial signals.
 2. Theradio apparatus according to claim 1, wherein the plurality of antennasare divided into a plurality of sub-arrays of antennas, each of thesub-arrays of antennas corresponding to one of the spatial signals. 3.The radio apparatus according to claim 1 21, wherein the signalprocessing unit is configured to change a combination of the antennasallocated to each of the sub-arrays of antennas.
 4. The radio apparatusaccording to claim 3, wherein the radio apparatus further comprisesmonitor means for monitoring communication quality for each spatialsignal during communication, and the control means is configured tochange the number of the antennas allocated to each of the sub-arrays inaccordance with a detection result of the monitor means.
 5. The radioapparatus according to claim 1, wherein the information on the number ofspatial signals is transmitted before the communication with the anotherradio apparatus is started.
 6. The radio apparatus according to claim 1,wherein the information on the number of spatial signals is transmittedat a control information stage during establishing the traffic channel.7. The radio apparatus according to claim 2 21, wherein a MIMO channelis set for each of the sub-arrays for communication with the anotherradio apparatus.
 8. The radio apparatus according to claim 2 21, whereinthe signal processing unit is configured to determine the a number ofthe plurality of sub-arrays based on the a number of spatial signalsnotified by a the another radio base station apparatus.
 9. The radioapparatus according to claim 2, wherein the control means is configuredto allocate one of the plurality of antennas to each of the sub-arraysin a number corresponding to the number of signals notified by a radiobase station apparatus and subsequently, to allocate the remainingantennas to each of the sub-arrays in a prescribed order.
 10. The radioapparatus according to claim 2 21, wherein each of the sub-arrays isallocated antennas having an identical plane of polarization.
 11. Theradio apparatus according to claim 1 21, further comprising means fordetecting a reception level for each antenna, wherein the antennas areallocated to each of the sub-arrays based on the detected receptionlevel.
 12. A radio apparatus for communication by forming a plurality ofspatial signals to another radio apparatus, comprising: a plurality oftransmission units connectable to a plurality of antennas; a signalprocessing unit capable of processing spatial signals to be transmittedthrough the plurality of transmission units and the plurality ofantennas; a storage unit that stores in advance information on thenumber of spatial signals that can be processed by the signal processingunit, wherein the number of spatial signals is smaller than or equal tothe total number of the plurality of antennas; a control unit thatcontrols a process of transmitting the information on the number ofspatial signals.
 13. The radio apparatus according to claim 12, whereinthe plurality of antennas are divided into a plurality of sub-arrays ofantennas, each of the sub-arrays of antennas corresponding to one of thespatial signals.
 14. The radio apparatus according to claim 12 24,wherein the signal processing unit is configured to change a combinationof the antennas allocated to each of the sub-arrays of antennas.
 15. Theradio apparatus according to claim 14, wherein the radio apparatusfurther comprises a monitor unit that monitors communication quality foreach spatial signal during communication, and the control unit isconfigured to change the number of the antennas allocated to each of thesub-arrays in accordance with a detection result of the monitor unit.16. The radio apparatus according to claim 12, wherein the informationon the number of spatial signals is transmitted before the communicationwith the another radio apparatus is started.
 17. The radio apparatusaccording to claim 12, wherein the information on the number of spatialsignals is transmitted at a control information stage duringestablishing the traffic channel.
 18. The radio apparatus according toclaim 13 24, wherein a MIMO channel is set for each of the sub-arraysfor communication with the another radio apparatus.
 19. The radioapparatus according to 13 24, wherein the signal processing unit isconfigured to determine the a number of the pluraity of sub-arrays basedon a the number of available signals notified by a the another radiobase station apparatus.
 20. The radio apparatus according to claim 13,wherein the control unit is configured to allocate one of the pluralityof antennas to each of the sub-arrays in a number corresponding to thenumber of signals notified by a radio base station apparatus andsubsequently, to allocate the remaining antennas to each of thesub-arrays in a prescribed order.
 21. A radio apparatus for multiplexedcommunication by forming a plurality of spatial signals to another radioapparatus, comprising: a plurality of transmission units connectable toa plurality of antennas, wherein the plurality of antennas are dividedinto a plurality of sub-arrays of antennas, each of the sub-arrays ofantennas corresponding to one spatial signal; at least a signalprocessing unit capable of processing spatial signals to be transmittedthrough the plurality of transmission units and the plurality ofsub-arrays of antennas; storage means for storing prior to any requestto establish a link channel being sent to the another radio apparatusinformation on a number of available spatial signals that can beprocessed by the signal processing unit, wherein the number of availablespatial signals is smaller than or equal to a total number of theplurality of sub-arrays of antennas; and control means for controlling aprocess of transmitting the information on the number of availablespatial signals in a link request to the another radio apparatus,wherein the control means is configured to allocate one antenna of theplurality of antennas to each of the sub-arrays in a numbercorresponding to a number of spatial signals transmitted to the anotherradio apparatus and subsequently, to allocate remaining antennas of theplurality of antennas to each of the sub-arrays in a prescribed order.22. The radio apparatus according to claim 21, wherein the informationon the number of available spatial signals is transmitted in a linkrequest from the radio apparatus before the multiplexed communicationwith the another radio apparatus is started.
 23. The radio apparatusaccording to claim 21, wherein the information on the number ofavailable spatial signals is transmitted at a control information stageduring establishing the traffic channel.
 24. A radio apparatus formultiplexed communication by forming a plurality of spatial signals toanother radio apparatus, comprising: a plurality of transmission unitsconnectable to a plurality of antennas, wherein the plurality ofantennas are divided into a plurality of sub-arrays of antennas, each ofthe sub-arrays of antennas corresponding to one spatial signal; a signalprocessing unit capable of processing spatial signals to be transmittedthrough the plurality of transmission units and the plurality ofsub-arrays of antennas; a storage unit that stores prior to any requestto establish a link channel being sent to said another radio apparatusinformation on a maximum number of available spatial signals that can beprocessed by the signal processing unit, wherein the maximum number ofavailable spatial signals is smaller than or equal to a total number ofthe plurality of sub-arrays of antennas; a control unit that controls aprocess of transmitting the information on the maximum number ofavailable spatial signals, wherein the control unit is configured toallocate one antenna of the plurality of antennas to each of thesub-arrays in a number corresponding to a number of available spatialsignals notified by the another radio apparatus and subsequently, toallocate remaining antennas of the plurality of antennas to each of thesub-arrays in a prescribed order; and wherein the information on themaximum number of available spatial signals is transmitted in a requestto establish a link from said radio apparatus to said another radioapparatus.
 25. The radio apparatus according to claim 24, wherein theinformation on the maximum number of available spatial signals istransmitted before the multiplexed communication with the another radioapparatus is started.
 26. The radio apparatus according to claim 24,wherein the information on the maximum number of available spatialsignals is transmitted at a control information stage duringestablishing the traffic channel.